<a href="#" class="scrollup" style="display: inline;"></a>

.scrollup {
    width: 140px;
    height: 151px;
    position: fixed;
    bottom: 2%;
    right: 1%;
    display: none;
    text-indent: -9999px;
    background: url(/img/sctop.png) no-repeat;
    z-index: 21;
}

<script type="text/javascript">
$(document).ready(function() {
    $(window).scroll(function() {
        if ($(this).scrollTop() > 800) {
            $('.scrollup').fadeIn();
        } else {
            $('.scrollup').fadeOut();
        }
    });
    $('.scrollup').click(function() {
        $("html, body").animate({
            scrollTop: 0
        }, 600);
        return false;
    });
});
</script>